RPM Lite is a FREE, supported Rails production monitoring product that helps you keep your app humming. You get deep, real-time visibility into your app, so you always know what’s up. Use it on as many applications and hosts as you like. For as long as you like.

Troubleshoot in development. Troubleshoot in production. Build high speed into your app from the very beginning.

Sign up for New Relic (its free!!)

I spent two minutes checking it out with the *small flex/rails app that i made the other day. What i liked straight off the bat was two things:

1. Installing the plugin: Easy as pie! I’m not exactly sure if you can install it without signing up, nevertheless it was a cinch!
2. Point and Go!: All you got to do is point your browser to:
   http://localhost:3000/newrelic and you are done!!

So its pretty much a straight outta the box type of deal here. Will definitely be using this little baby from now on!